I would still argue that you did not use far too much insulin.I used far too much insulin that the NHS has to fund on rubbish that is harmful to my health rather than wholesome food to nourish my body
I would also argue that it is important to nourish your mind as well as your body. *If* you got some enjoyment from that chocolate, it was wholesome to your mind and nourishing your overall mind and body.
I would definitely not beat yourself up for having more insulin than you usually do - if you are anything like me, it is balanced out by the days when you take less insulin than others.
I am sure the NHS budget for us to take more insulin than we do and certainly wouldn't want us rationing it as is necessary in other countries.
I appreciate you value the need to keep on the straight and narrow (and that your "Bad Girl" was slightly tongue in cheek) but please be nice to yourself and maybe change it to "fully" tongue in cheek rather than "slightly".